Lecture 3 Plate Tectonics and the Rock CycleQuestions to PonderPlate tectonics1. Divergent boundarySlide 5Slide 6Slide 7Slide 8Features of Divergent boundaries2. Convergent boundaryContinental crust then is more buoyant than oceanic crustSubduction v. CollisionSlide 13Slide 14Slide 15Slide 16Features of Convergent boundaries3. Transform boundarySlide 19Slide 20Transform boundaries, comparedFeatures of Transform boundariesThe movement of plates, creation of new crust, and subduction of old crust makes earth “Dynamic”Evidence of Plate tectonics:Slide 25Slide 26Slide 27Slide 28Slide 29Slide 30Slide 31Slide 32Previous arguments for continental “drift”Slide 34Slide 35Slide 36Slide 373 rock classificationsSlide 39Slide 40Rock typesWhat are Rocks…What is a mineral and why do we care….States of Matter (anything that has mass and occupies space)MineralsLecture 3Plate Tectonics and the Rock CycleQuestions to Ponder•What evidence exists to support Plate tectonics?•How does plate tectonics affect earth?•How does rock formation and rock destruction relate to Plate tectonics?Plate tectonics1. Divergent boundary•Spreading apart – new crust is usually made at such boundariesMid Ocean RidgeMid Ocean Ridge system actually extends onto continental crust!Features of Divergent boundaries•In oceans–Volcanism–Undersea mountain ranges (ridges)•On continents–Some volcanism–Rift valleys2. Convergent boundary•Plates move towards one another•Because either of the two crust types is involved we get 3 subcategories•A. Oceanic-continental crust–Subduction•B. Oceanic-oceanic crust–Subduction•C. Continental to continental crust–CollisionContinental crust then is more buoyant than oceanic crustSubduction v. Collision•Subduction–Denser crust dives (subducts) under less dense crust–Oceanic crust subducts under continental crust–Older (cooler and more dense) oceanic crust subducts under younger (warmer and less dense) oceanic crust•Collision – continental to continental crust–Neither subducts under one anotherSubduction: The Islands of Japan(Also the Aleutians; Caribbean; Indonesia…)Subduction – the Andes in South AmericaCollision – the Himalayas in India/TibetFeatures of Convergent boundaries•Subduction zone–Volcanism (New rocks)–Earthquakes–Island Arcs–Mountain ranges (Volcanic in origin)•Collision–Earthquakes–Mountain ranges3. Transform boundary–Plates move laterally past each other–Commonly associated with mid-ocean rift systems•Space accommodation–Continental zones•San Andreas FaultLateral motionTransform boundaries, comparedFeatures of Transform boundaries•Earthquakes. (duh!)The movement of plates, creation of new crust, and subduction of old crust makes earth “Dynamic”Evidence of Plate tectonics:•Modern distribution of volcanoes, mountain building, earthquakesEvidence of Plate tectonics:•Modern distribution of volcanoes, mountain building, earthquakes•Magnetic orientation of minerals in rocksMagnetic Striping on SeafloorIn the 1950s, the Atlantic seafloor was found to consist of alternating stripes of normal and reversely magnetized rocksEvidence of Plate tectonics:•Modern distribution of volcanoes, mountain building, earthquakes•Magnetic orientation of minerals in rocks•Ages of rocks at divergent boundariesSeafloor SpreadingA Mid Ocean Ridge is a divergent zone where hot magma rises up, cools and solidifies, forming new basaltRocks get equally older with equal distance from the MORPrevious arguments for continental “drift”•Continental “Fit”•Mountain ranges of similar ages and rock types on distant continents•Evidence of preferred glacial movement on separate continents•Fossil distribution•But, early proponents had no viable mechanism to explain this movement!Magnetic rocks of different ages on the same continent can point to very different apparent magnetic pole positionsSo either the poles are wandering or the continents are movingPolar WanderingThe role of Plate Tectonics to Rock formation3 rock classificationsTextbook recognizes a 4th classification:Hydrothermal RocksRocks are continuously Formed,Broken down, and Altered.Earth Recycles!Rock CycleTemperature &PressureRock types•Igneous–Volcanic (Extrusive)–Plutonic (intrusive)•Sedimentary–Clastic detrital–Chemical precipitates•Metamorphic–Regional–ContactWhat are Rocks…•Aggregate of mineralsWhat is a mineraland why do we care….•A mineral is:“Naturally occurring, inorganic solid with a specific chemical formula and definite crystal structure”Further, minerals are the basic building block of rocks (!!!!), as well as often being critical resources, themselves.Thus, we have to understand a bit of chemistry…..States of Matter(anything that has mass and occupies space)•Solid–Crystalline - atoms bond together in a regular orderly pattern–Amorphous - atoms bonded together in a random pattern•Liquid - atoms or molecules tightly packed but in random motion•Gas - particles in random motion at high speeds, separated by empty spaceMinerals•Naturally occurring inorganic solid, with a definite crystal structure and specific chemical formula–Must be solid with a crystal structure•Ice vs. water–Must be formed by a natural process•Natural vs. synthetic diamonds–Must be an inorganic compound•Coal is not a